1. Field of the Art
This invention relates to rapid production of alcoholic beverages such as, for example, beer and wine. More particularly, the present invention pertains to rapid process for production of alcoholic beverages with low concentration of diacetyls.
The production steps of alcoholic beverages generally consist essentially of the earlier stage of fermentation wherein fermentation proceeds with proliferation of yeast in the starting brew liquor in which yeast is added, and, subsequent thereto, the later stage of fermentation wherein fermentation proceeds without proliferation of yeast. In the earlier stage of fermentation, simultaneously with progress of consumption by the yeast of both nitrogen and carbon which are substrates for the yeast, diacetyls (in the present invention, the term "diacetyls" refers to comprehensively vicinal diketones such as diacetyl, pentanedione, etc. and acetohydroxyacids which are precursors thereto, such as acetolactic acid, acetohydroxybutyric acid, etc.) of which by-production should be avoided will inevitably be formed. On the other hand, consumption of the carbon takes place mainly in the later stage of fermentation, and the later stage is also the step of making diacetyls formed in the earlier stage of fermentation disappear.
The diacetyls which have come to exist in the fermented liquor in the earlier state of fermentation are mostly vicinal diketone precursors, which cannot be decomposed as such by the microorganism employed, namely yeast, but they can be decomposed for the first time when they are converted to vicinal diketones. However, since the reaction in which a vicinal diketone precursor is converted into a vicinal diketone is a non-biological and purely chemical reaction, and the velocity of this chemical reaction is slow, because the later stage of fermentation is conducted at relatively lower temperature, and the reaction stands as a velocity controlling factor, whereby a long time is necessary for production of alcoholic beverages having a low concentration of diacetyls.
2. Prior Art
For shortening of brewing time and lowering of concentration of diacetyls, various proposals have heretofore been made in the art.
For example, as a means for producing rapidly alcoholic beverages, it was proposed to increase the concentration of yeast which serves to effect fermentation [J. Inst. Brew., 72, 193 (1966); and ibid, 75, 260 (1969)]. However, the fermented liquor in that case has high diacetyl concentration, whereby aging for a long time is stated to be required [Amer. Soc. Brew. Chem. Proc., 36, 9 (1978)].
Meanwhile, the techniques for immobilizing yeast in hydrogels have been advanced, and a brewing method employing such immobilized yeast has been proposed [J. Inst. Brew., 84, 228 (1978), EBC Congress Proc., 505 (1981) and Brauwissenschaft, 35, 254 (1982)]. This method, which can employ yeast at a high concentration, enables shortening of the brewing period as an advantage of the above high concentration method, and therefore expected to be promising as a brewing technique in the future. However, this method cannot be free from the problem inherent in the high yeast concentration method, namely high concentration of diacetyls in the fermented liquor formed, and therefore its application has not yet come to practice because of a long time of aging required.
Alcoholic beverages having a high concentration of diacetyls have disagreeable odor called "diacetyl odor". The diacetyl odor has a threshold value for organoleptic perception so low as 0.1 to 0.2 mg/liter and has thus been hated by brewers as impurities which impair flavor of alcoholic beverages.
In view of this, various methods have heretofore been proposed to reduce the quantity of once-formed diacetyls such as, for example, subjecting the alcoholic beverage produced to post fermentation. In addition, methods for suppressing formation of diacetyls have also been proposed, such as conducting fermentation step under aeration, at an elevated temperature or at a low pH as shown in, for example, THE BREWER, December 1974, pp 638-643.
These methods, however, are not satisfactory because the alcoholic beverages so produced are not fully acceptable due to their poor flavor, and it has thus been resorted to to carry out the later stage of fermentation in a long period of time so as to cause the diacetyls to disappear although such a long fermentation is disadvantageous.
An attempt to reduce diacetyls in the fermented liquor obtained by the immobilized yeast method by heating has also been reported (J. Inst. Brew., 79, 487, 1973). The fermentation within a bed of immobilized yeast should suffer from another problem such that, since consumption by the yeast used of .alpha.-amino nitrogen in a fermentation liquor does not fully take place, the fermented liquor obtained has a high concentration of .alpha.-amino nitrogen or has a low concentration of flavor components produced as a result of consumption of .alpha.-amino nitrogen.